Display screen or portion thereof with transitional computer graphical user interface



FIG. 1 is a front view of the first image in a sequence of a display screen or portion thereof with transitional computer graphical user interface, according to a first embodiment of the new design;

FIG. 2 is the second image thereof;

FIG. 3 is a front view of the first image in a sequence according to a second embodiment of the new design;

FIG. 4 is the second image thereof;

FIG. 5 is a front view of the first image in a sequence according to a third embodiment of the new design; and,

FIG. 6 is the second image thereof.

The appearance of the transitional image sequentially transitions between the images shown in FIGS. 1-2, FIGS. 3-4 and FIGS. 5-6, respectively. The process or period in which one image transitions to another image forms no part of the claimed design.

The gray shading portrays a contrast in appearance.

The longer broken lines showing a portion of an electronic device illustrate environmental subject matter. The intermediate-length broken line showing a display screen, the shorter broken lines showing a portion of the display screen, and all other broken lines showing features of the graphical user interface are included for the purpose of illustrating portions of the article. The broken lines form no part of the claimed design. 

CLAIM The ornamental design for a display screen or portion thereof with transitional computer graphical user interface, as shown and described. 